Mercury Contamination in Riverine Sediments and Fish Associated with Artisanal and Small-Scale Gold Mining in Madre de Dios, Peru

Abstract

Artisanal and small-scale gold mining (ASGM) in Madre de Dios, Peru, continues to expand rapidly, raising concerns about increases in loading of mercury (Hg) to the environment. We measured physicochemical parameters in water and sampled and analyzed sediments and fish from multiple sites along one ASGM-impacted river and two unimpacted rivers in the region to examine whether Hg concentrations were elevated and possibly related to ASGM activity. We also analyzed the 308 fish samples, representing 36 species, for stable isotopes (δ15N and δ13C) to estimate their trophic position. Trophic position was positively correlated with the log-transformed Hg concentrations in fish among all sites. There was a lack of relationship between Hg concentrations in fish and either Hg concentrations in sediments or ASGM activity among sites, suggesting that fish Hg concentrations alone is not an ideal bioindicator of site-specific Hg contamination in the region. Fish Hg concentrations were not elevated in the ASGM-impacted river relative to the other two rivers; however, sediment Hg concentrations were highest in the ASGM-impacted river. Degraded habitat conditions and commensurate shifts in fish species and ecological processes may influence Hg bioaccumulation in the ASGM-impacted river. More research is needed on food web dynamics in the region to elucidate any effects caused by ASGM, especially through feeding relationships and food sources.

Elevated Hair Mercury Levels Are Associated With Neurodevelopmental Deficits in Children Living Near Artisanal and Small‐Scale Gold Mining in Peru

“…Taken together, these results suggest that mercury exposures may be harming the development of children living in an ASGM region and that the effects may be most pronounced among native children. Although this study does not directly link child mercury exposure to gold mining, research in Madre de Dios has suggested a strong causal link between artisanal mining, increased release of mercury into the watershed (i.e., either directly from mining or increased erosion and release of natural mercury), and increased bioaccumulation of methylmercury in fish (e.g., Diringer et al, 2015; Martinez et al, 2018). This, combined with studies linking increased hair mercury levels to fish consumption in the same communities (e.g., Feingold et al, 2019; Fréry et al, 2001; Wyatt et al, 2017), provides consistent evidence for the link between neurocognitive impairment originating from mercury exposure and ASGM in the region.…”

Deforestation and Forest Degradation Due to Gold Mining in the Peruvian Amazon: A 34-Year Perspective

“…Mining methods also likely have significant impacts on the amount of mercury pollution and how it behaves in the environment. Biogeochemical cycling, particularly the conversion between elemental and methylmercury, depends on transport, biotic communities, and anoxic conditions, and these in turn are all affected by mining type [47], though these dynamics are poorly understood.…”

Co-production of contaminated landscapes: anthropogenic loading and food web structure drive mercury bioaccumulation in abandoned gold mines

“…In the bottom sediments of these waterbodies, under certain abiotic conditions, inorganic mercury can undergo a microbially-mediated transformation into methylmercury, the most toxic and biologically available form of mercury (13)(14)(15). Many studies have documented bioaccumulation of mercury in the vicinity of active mines (16)(17)(18)(19), in sediments and tailings downstream of mining (20)(21)(22), and even legacy contamination from mines that have long been abandoned (23,24). Bioaccumulation of mercury can cause a wide range of detrimental impacts to wildlife such as a reduction in growth (25)(26)(27), juvenile survivorship (28), reproductive success (29,30), and even mortality (31).…”

“…However, these ponds are also potential hotspots where inorganic mercury can be transformed into methylmercury, and bioaccumulate in wildlife (24,39). In Madre de Dios, there is growing evidence that mercury contamination from ASGM extends beyond the boundaries of mining areas as high levels of total inorganic mercury (THg) have been documented in downstream river sediments (21,22), fish (16), indigenous populations upstream of mining (40), and in wildlife found far from mining areas (19). Further, we found that the type of technology used in gold production influenced the degree of mercury loading (as measured by sediment THg concentration), and together with differences in food-web structure across abandoned mines, these factors controlled the rate of mercury biomagnification at each site.…”